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+/* I/O block size definitions for coreutils
+ Copyright (C) 1989, 1991-2011 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+/* Include this file _after_ system headers if possible. */
+
+/* sys/stat.h will already have been included by system.h. */
+#include "stat-size.h"
+
+
+/* As of Mar 2009, 32KiB is determined to be the minimium
+ blksize to best minimize system call overhead.
+ This can be tested with this script with the results
+ shown for a 1.7GHz pentium-m with 2GB of 400MHz DDR2 RAM:
+
+ for i in $(seq 0 10); do
+ size=$((8*1024**3)) #ensure this is big enough
+ bs=$((1024*2**$i))
+ printf "%7s=" $bs
+ dd bs=$bs if=/dev/zero of=/dev/null count=$(($size/$bs)) 2>&1 |
+ sed -n 's/.* \([0-9.]* [GM]B\/s\)/\1/p'
+ done
+
+ 1024=734 MB/s
+ 2048=1.3 GB/s
+ 4096=2.4 GB/s
+ 8192=3.5 GB/s
+ 16384=3.9 GB/s
+ 32768=5.2 GB/s
+ 65536=5.3 GB/s
+ 131072=5.5 GB/s
+ 262144=5.7 GB/s
+ 524288=5.7 GB/s
+ 1048576=5.8 GB/s
+
+ Note that this is to minimize system call overhead.
+ Other values may be appropriate to minimize file system
+ or disk overhead. For example on my current GNU/Linux system
+ the readahead setting is 128KiB which was read using:
+
+ file="."
+ device=$(df -P --local "$file" | tail -n1 | cut -d' ' -f1)
+ echo $(( $(blockdev --getra $device) * 512 ))
+
+ However there isn't a portable way to get the above.
+ In the future we could use the above method if available
+ and default to io_blksize() if not.
+ */
+enum { IO_BUFSIZE = 32*1024 };
+static inline size_t
+io_blksize (struct stat sb)
+{
+ return MAX (IO_BUFSIZE, ST_BLKSIZE (sb));
+}